The effects of ionizing, ultraviolet radiation and ultrasound on cells and their constituents are being studied. The modification of radiation damage in DNA by cancer chemotherapy agents of the intercalating and alkylating types is of interest since such information is useful for combined modality treatment in radiation therapy. In relation to photodynamic therapy with hematoporphyrin derivative, we have studied the photosensitizing reactions of porphyrin derivatives. It was found that the spin trap 5,5 dimethyl-1-pyrroline-N-oxide is converted by certain photoexcited porphyrins to a characteristic Electron Spin Resonance (ESR) detectable species which is the product of singlet oxygen oxidation. Photolysis of certain metalloporphyrins at pH 11 lead to the formation of hydroxyl radicals detectable by spin trapping and ESR. The photodynamic action of adriamycin, daunomycin and mitoxantrone in the presence of peptides or nuclei acids was investigated. When adriamycin and daunomycin are photoirradiated in the presence of oxygen, superoxide anion radicals are generated, indicating that the photodegradation of DNA in the presence of these drugs is mediated by dissolved oxygen. New photosensitized reactions by several FDA certified food colors have been discovered. Continuing our studies of the effects of ultrasound on aqueous solutions, we have found that 1 microsecond pulses of 1 megahertz ultrasound bring about transient cavitation and the formation of OH and H radicals under diagnostic exposure conditions. Recently we have studied the feasibility of detecting free radicals in human red blood cells and V79 Chinese hamster cells by ESR and spin trapping. Generating radicals by Gamma -radiation or by adriamycin and using appropriate radical scavengers and line broadening agents it is possible to distinguish between endo and exo cellular formation of radicals.